The present invention concerns signal analysis and pertains particularly to display of code power in all symbol rates in a single screen for code-division multiple access signals employing layered orthogonal codes.
Code-division multiple access (CDMA) is a class of modulation that uses specialized codes to provide multiple communication channels in a designated segment of the electromagnetic spectrum. In 1994, the Telecommunications Industry Association (TIA) released the IS-95 and IS-97 standards which ensure the mobile station/base-station compatibility of cellular telephone systems which use dual-mode CDMA systems.
In order to measure the power, time, frequency, and phase of code domain signals, code domain analyzer systems are used. For example, the HP 83203B CDMA cellular adapter, available from Hewlett-Packard Company, having a business address of 3000 Hanover Street, Palo Alto, Calif. 94304, is designed to make the base station transmitter measurements specified in the IS-95 and IS-97 standards.
The measurement algorithms used by the HP 83203B CDMA cellular adapter provide a characterization of the code domain channels of a CDMA base station transmitter. One of the measurements, called code domain power, measures the distribution of power in the code domain channels. This measurement can be used to verify that the various channels are at expected power levels and to determine when one code domain channel is leaking energy into the other code domain channels. The crosscoupling of code domain channels can occur for many reasons. For example, time misalignment of the channels, can negate the orthogonal relationship among code domain channels. Additionally, impairment of the signals caused by nonideal or malfunctioning components in the transmitter can cause crosscoupling. To determine the quality of the transmitter signal, the HP 83203B CDMA cellular adapter measures a waveform quality factor, p. The waveform quality factor is the amount of transmitter signal energy that correlates with an ideal reference signal when only the pilot channel is transmitted. The results are shown in graphic form on a display of the HP 83203B CDMA cellular adapter. In prior art code domain analyzers, such as the HP 83203B CDMA cellular adapter, it has been possible to view code power for only a single symbol rate (code layer) per screen.
For further information on the general concepts of CDMA signals and measurements, the signal flow of the measurement algorithms used for CDMA signals, the specifications from the IS 97 standard and performance predictions for the measurement algorithms based on mathematical modeling and simulations, and some typical results of measurements, see Raymond A. Birgenheier, Overview of Code-Domain Power, Timing and Phase Measurements, Hewlett-Packard Journal, February 1996, pp. 73-93.